1. Field of the Invention
The present invention relates to particles, and their method of production, for use in particle-image velocimetry.
2. Description of the Related Art
It is known in the art to utilize single-point fluid flow velocity measurement techniques such as hot wire anemometry, laser doppler anemometry and the pitot tube to find the velocity only at a specific point. This makes flow analysis difficult in that flow structures are hard to clearly identify, and therefore it is arduous to obtain an overview of the flow since data interpretation is quite hard.
A possible solution is to make single point measurements at many different points in the flow field. However problems arise in data analysis. Due to the cost of laser doppler anemometry, it is nearly impossible to acquire point measurements at more than a few points. Hence, there is much room for interpretive analysis of the data in which the results are largely based on "educated guessing". Further, with all single point measuring techniques other than laser doppler anemometry, the methods alter the flow that they are intended to measure.
Another known method to measure flow velocity is to perform quantitative flow visualization, i.e. performing measurements over the entire field. In prior methods, particles that are reflective have been relied upon. The reflected intensity was usually weak and it was difficult to photograph the trails of the particles. To attack this problem, it was necessary to utilize a more intense laser beam and/or larger particles to strengthen the reflected light.
However, it is desirable to use as small a particle as possible and as weak a laser. A weak laser is desirable due to safety and cost considerations. The particles should be smaller than any scale of turbulence so as not to alter the flow and yet be detectable and be capable of photographic recordation. If the particles are larger than any significant turbulence scale, different portion of the same particle are exposed to different velocities. Further, too large a particle will tend to alter the flow it was intended to measure. The particles must also be neutrally buoyant, otherwise they will move relative to the fluid as a result of gravity and/or pressure gradients.
Hence, it was necessary to develop particles that were small and used a different tracing method than light reflection.